From: Mel Gorman Date: Wed, 5 May 2021 01:39:30 +0000 (-0700) Subject: mm/memory_hotplug: remove broken locking of zone PCP structures during hot remove X-Git-Tag: accepted/tizen/unified/20230118.172025~7280^2~19 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=8ca559132a2d9b56732d35e2b947af96acb9b80b;p=platform%2Fkernel%2Flinux-rpi.git mm/memory_hotplug: remove broken locking of zone PCP structures during hot remove zone_pcp_reset allegedly protects against a race with drain_pages using local_irq_save but this is bogus. local_irq_save only operates on the local CPU. If memory hotplug is running on CPU A and drain_pages is running on CPU B, disabling IRQs on CPU A does not affect CPU B and offers no protection. This patch deletes IRQ disable/enable on the grounds that IRQs protect nothing and assumes the existing hotplug paths guarantees the PCP cannot be used after zone_pcp_enable(). That should be the case already because all the pages have been freed and there is no page to put on the PCP lists. Link: https://lkml.kernel.org/r/20210412090346.GQ3697@techsingularity.net Signed-off-by: Mel Gorman Acked-by: Michal Hocko Reviewed-by: Oscar Salvador Cc: "Michael S. Tsirkin" Cc: Vlastimil Babka Cc: Alexander Duyck Cc: Minchan Kim Cc: David Hildenbrand Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 81db389..b012805 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -9020,12 +9020,9 @@ void zone_pcp_enable(struct zone *zone) void zone_pcp_reset(struct zone *zone) { - unsigned long flags; int cpu; struct per_cpu_pageset *pset; - /* avoid races with drain_pages() */ - local_irq_save(flags); if (zone->pageset != &boot_pageset) { for_each_online_cpu(cpu) { pset = per_cpu_ptr(zone->pageset, cpu); @@ -9034,7 +9031,6 @@ void zone_pcp_reset(struct zone *zone) free_percpu(zone->pageset); zone->pageset = &boot_pageset; } - local_irq_restore(flags); } #ifdef CONFIG_MEMORY_HOTREMOVE